This represents a continuation of a long-term prospective study of radiation-induced carcinogenesis in three human populations: the first, persons who were treated in infancy with x-rays for alleged enlargement of the thymus gland; the second, women who received x-ray treatments to the breasts for post-partum mastitis; and the third, persons given x-ray and/or radium treatments to the head in early childhood for lymphoid hyperplasia of the nasopharynx. Health data are collected by mail questionnaire from treated persons and from their untreated sibling controls. Significant reported illnesses are verified through the attending physician and hospital. Histological reviews are performed on slides from tumors of primary interest in the studies. A program of mammographic-thermographic screening of the women who received breast irradiation will be repeated. In addition, a sample of their untreated sisters (controls) who meet NCI recommended eligibility requirements for mammographic-thermographic screening will also be examined. The objectives of the program are (1) to determine the qualitative nature of and quantitative risk of radiation-induced neoplastic disease and of conditions with abnormal immunological features, and (2) to effect by screening the early diagnosis and treatment of breast cancer in a high-risk population.